Dissociative identity disorder (DID, commonly referred to as multiple personality disorder) is well known to the general public through multiple movies and books. However, the disease remains poorly understood and rather mysterious for the medical specialists. The definition of this disorder implies that a patient has at least two distinctive and relatively long-lasting identities (sometimes called “alters”) that manifest themselves in a person’s behavior. Their presence is accompanied by memory impairments that cannot be explained by usual forgetfulness.

However, there are no clear clinical criteria to help in the diagnostics. There is a whole range of dissociative disorders that range from daydreaming and lapses in attention to serious pathologies. The diagnostics rely on descriptive data rather than something measurable. This leads to lots of confusion, controversies, and inconsistencies.

Historically, the incidence of multiple personality disorder varied wildly. For a long time, the condition was considered among the rarest psychological disorders, with less than 100 cases described before 1944. The incidence of DID rose sharply in the 1970s–1980s, reaching 20,000 by the end of the century. In addition, this growth was accompanied by the increase in the number of alters reported in patients, from just one to 13–16 by the 1980s. These changes in the statistics might have been caused by increasing recognition of the disease symptoms among practitioners, but also led to the growing skepticism in the research community about the very existence of this distinct condition.

The variability on the geographic distribution of this condition is substantial too: the disorder is diagnosed in the US much more frequently than anywhere else. The overwhelming majority of publications on this condition originate from North America, making some researchers believe that DID is a purely American disease confined to this continent. This further adds to the skepticism of many health practitioners: there are no reasons to believe that qualified specialists capable of recognizing this condition are vastly underrepresented in other developed countries.

There is little clarity regarding what causes the disorder. The iatrogenic hypothesis suggests that DID can be a result of psychotherapeutic treatment, while the traumatogenic hypothesis states that the disease develops as a result of severe trauma, usually in childhood. Some researchers believe that most cases of DID are pseudogenic, i.e., simulated. There is an opinion that many patients want to believe that they have the disorder, to explain the inconsistencies in their own behavior.

The incidence of DID is 5–9 times higher in females compared to males. Again, there is no agreement among specialists regarding what causes such a big gender difference.

The potential reasons for the sharp increase in the incidence of DID were examined in the scientific literature. Although there are many possible explanations for this phenomenon, the iatrogenic explanation appears to be the most substantiated. The unusually large number of diagnosis in the 1980s were clustered around a small number of practitioners, many of whom used hypnosis as a therapeutic tool. It is quite possible that under the influence of hypnosis the patients with a higher level of suggestibility may start to believe that they are suffering from split personality disorder, and behave accordingly. The level of hypnotisability of people with the diagnosis of DID is known to be the highest among any clinical population.

The rise of the DID diagnosis numbers also correlated with the growing number of split personality cases in the criminal court cases. The defense on the basis of DID was rarely successful, as it was often assumed that the defenders simply pretend to have the disorder to avoid taking responsibility for their crimes.

An opinion exists that the manifestations of DID are simply the consequences of other disorders such as bipolar disorder, schizophrenia, and borderline personality disorder. Many patients diagnosed with DID have previous history of these and other psychiatric conditions. Another theory suggests that the manifestations of DID are the consequences of trauma. There is plenty of clinical cases in support of this theory, but not so much statistical data.

Importantly, there is a shortage of proper neurological studies of this disorder. Nobody knows what exactly causes it and what kind of changes take place in the brains of patients diagnosed with this disease. The brain imaging data from patients with DID do not reveal any specific diagnostic patterns. Several studies demonstrated that the changes in personality state in the DID patients are associated with certain changes in the blood flow in the brain. There are also differences in the brain blood flow patterns between patients with DID and healthy control subjects. It remains uncertain if these differences can be used in the diagnostics.

The question of how real the majority of DID cases are is yet to be fully answered. In general, researchers agree that there are cases with very pronounced and obvious manifestations that would be rather hard to explain without invoking the concept of DID. However, when it comes to less severe cases, the diagnostic remains really problematic. This creates a problem for patients, as not knowing the specific diagnosis means the lack of clarity with treating the problem. Also, there is no consensus regarding how to treat the split personality disorder. Various psychotherapeutic and hypnotherapeutic techniques are currently used, but their efficacy remains unknown due to the absence of controlled randomised clinical trials. Clearly, there is a lot of room for further research in this field.

Viatcheslav Wlassoff, PhD, is a scientific and medical consultant with experience in pharmaceutical and genetic research. He has an extensive publication history on various topics related to medical sciences. He worked at several leading academic institutions around the globe (Cambridge University (UK), University of New South Wales (Australia), National Institute of Genetics (Japan). Dr. Wlassoff runs consulting service specialized on preparation of scientific publications, medical and scientific writing and editing (Scientific Biomedical Consulting Services).

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